The present application contains references to other publications. These publications are incorporated herein by reference.
Celiac disease is defined as a disease of the small bowel caused by a permanent intolerance to gluten. Most common symptoms of the disease are weight loss due to malabsorption, diarrhea, anemia, and growth failure. Celiac disease affects people of all ages and gender. Its incidence is on the rise worldwide due to environmental and genetic factors, currently affecting, on average, 1/300 people (children and adults) in the United States and in other developed nations. Up until recently celiac disease was considered a disease affecting predominantly people of Northern European origin this, however, is changing as cases are now reported in Asia and the Middle East, albeit at a much lower rate.
Definitive diagnosis of the disease is made on the basis of small bowel biopsies obtained while the patient is on gluten containing diet and after the patient is taken off gluten and free of symptoms. While small bowel biopsy is an invasive diagnostic modality there are other diagnostic methods currently available.
Currently available blood serum tests (Table 1) take place in centralized laboratories and measure antibodies to antigens produced in the patient's body due to gluten intolerance. Results are usually available in several days to a few weeks.
TABLE 1Diagnostic blood tests for the diagnosis of celiac diseaseTestTechnologySensitivitySpecificityAnti-tTG antibodyELISA99%>90% IgA anti-Direct90%99%endomysial antibodyImmunofluerescenceAnti-gliadinELISALessLessantibodyDirectsensitivesensitiveImmunofluerescenceAnti-deamidatedExperimentalgliadin antibodyHLA-DQ2HLA typing94%73%HLA-DQ8HLA typing12%81%
In addition to blood testing for the presence of specific antibodies, as described in Table 1, blood serum can be tested for the presence of D-xylose, a sugar detected in serum one hour after the ingestion of carbohydrates. The D-xylose test is performed less frequently due to low sensitivity and specificity for the diagnosis of celiac disease and due to the broad use of the more specific antibody diagnostic tests.
Breath testing for the diagnosis of celiac disease has been investigated but is not currently used as a standard diagnostic method due to lower sensitivity (88%) and specificity (84%) when compared to the serum antibodies (Table 1). Tveito K. et al. (1) claim that 13C-xylose and 14C-xylose breath tests are diagnostic of celiac disease patients and both tests demonstrate high sensitivity (88%) and specificity (84%). These investigators also claim that the 13C-sorbitol breath test (2) for the diagnosis of celiac disease is superior to H2-sorbitol test due to higher sensitivity and specificity, however well below the specificity/sensitivity of 13C-xylose breath test. All of these breath tests require the patient to ingest a carbohydrate substrate, either xylose or sorbitol and undergo breath testing every 30 minutes starting one hour post ingestion up to four hours post ingestion of the substrate. Hryniuk A et al. (3) who investigated the presence of volatile alcohols in the breath of patients with celiac disease report that no differences were found in the breath levels of methanol, propanol, butanol, heptanol or hexanol investigated using chemical ionization of breath air with H3O+ and/or NO+ precursor ions in patients with celiac disease when compared to health subjects. All of the above described breath tests are based on spectroscopic analysis of the human breath content and take place at centralized laboratories. Rana, S V et al. (4) report that, at baseline, patients with celiac disease have significantly higher hydrogen in their breath than patients with functional bowel disease and normal subjects. Hydrogen breath test is a standard diagnostic modality for the diagnosis of lactose intolerance and other carbohydrate malabsorption but not for the diagnosis of celiac disease. The existing methodology for the detection of hydrogen in human breath in patients with lactose intolerance and bacterial overgrowth is through gas chromatography (Quintron Instrument Company).